Heat-treating apparatus for diffusion coating



April 18, 1967 SHOGO IZUMI 3,314,394

HEAT-TREATING APPARATUS FOR DIFFUSION COATING lFiled Oct. 21, 1965 JL/ J United States Patent 3,314,394 HEAT-TREATKNG APPARATUS FOR DIFFUSION COATING Shogo Izumi, Nishinomiya, Japan, assignor to Nippon Karoraizu Kogyo Kabushikikaisha, Osaka, Japan Filed Oct. 21, 1963, Ser. No. 317,655 2 Claims. (Cl. 11848) This invention relates to heat treating apparatus for diffusion coating processes.

Diffusion-coating of the surface of iron or steel with aluminum, chromium, silicon or any other non-ferrous metal is known as colorizing, chromizing or siliconizing. In diffusion-coating processes, it is important to produce a diffusion layer (which may be called an impregnated alloy layer) on the surface of iron or steel uniformly in thickness ,and content of the diffused metal. For that purpose, a process has been proposed in which a container charged with an impregnating agent and an article to be processed, is statically placed in a heating furnace, heated, and then gradually cooled after which the article in the container is removed.

Such a known process has a number of disadvantages which are enumerated as follows:

(1) During the heating, the temperature distribution for the container is non-uniform. The temperature rise will be non-uniform especially above and below, in front and to the rear of or to the right and left of the container whereby the difiusion layer will be adversely influenced and a uniform alloy layer will not be obtained.

(2) The container must be put into or removed from the heating furnace only after the furnace has cooled. That is to say, a long operating cycle is required and much fuel will be wasted.

(3) The furnace body is likely to be damaged by the repetition of heating cooling.

(4) Due to non-uniform heating, a thermal strain will occur in the container which may therefore be deformed. Thus, difficulty is experienced in repeated use of the container. Further, it takes such a long time to reach the required temperature from the cold furnace body that the wear of the outside surface of the container will be high.

The present apparatus eliminates the above mentioned disadvantages whereby the operating time is reduced, fuel saved and an excellent diffusion layer for-med. According to the invention, there is provided a heat-treating apparatus for diffusion-coating comprising a conveying means for conveying a tubular container charged with both an article to be processed and an impregnating agent while rotating the container about its axis as a center, a heating means for heating the container during rotation and positioned after the conveying means and a cooling means for cooling the said heated container positioned after the said heating means.

In the accompanying drawings:

FIGURE 1 is a side view of one embodiment of the present invention, in which a tubular container is shown in axial section,

FIGURE 2 is a plan view of the embodiment shown in FIGURE 1,

FIGURE 3 is a side view showing a modification of a heating furnace,

FIGURE 4 is a side view of another embodiment of the present invention, 7

FIGURE 5 is a plan view of rolls for conveying while rotating a tubular container around its axis as a center, and

FIGURE 6 is a sectional view of a heating furnace.

Firstly, the case of chromizing is explained and in the drawings, 1 is a tubular container, namely, a steel pipe having a 15.2 cm. outside diameter and being 5 meters in length. Base end 2 of the tubular container 1 is sealed and a steel plate 3, which is the article to be processed, and a mixture of a chromium powder and an alumina powder with the addition of a small amount of ammonium chloride as an impregnating agent are inserted into the container 1 through open end 5 as illustrated. Open end 5 of the pipe .is then sealed as at 6 with a mortar brick which serves as an exhaust port for the gas produced in the container. The container thus charged with the contents is horizontally placed on rolls 8 arranged on a base 7. The rolls 8 are drum-shaped and arranged diagonally to the direction of movement of the container 1. Thus, the container 1 will be gradually conveyed toward a heating furnace while rotating on its longitudinal axis.

After the conveying means a heating means is provided and 10 denotes a heavy oil heating furnace in which the temperature is kept at 1,200 C. by heavy oil introduced through a nozzle 11 and the heating zone is 1.5 meters long. Several of these heating furnaces may be arranged as illustrated in FIGURE 3 and in such a case, a roll 8 may be also provided between the furnaces.

After this heating means a cooling means is provided so that the container leaving the heating furnace 10 may be cooled by being sprayed with water by a shower type water cooler 12.

The process of chromizing by using the present apparatus will now be explained.

The container 1 charged with the contents as described above is conveyed at a velocity of 350 mm. per hour while being gradually rotated at a rate of one revolution every 4 minutes. The temperature Within the heating furnace is kept at l,200 C. (1,100 C. in the case of aluminum and 1,000 C. in the case of silicon) without being cooled. The container 1 is gradually inserted into the furnace from the open end sealed as at 6 with the mortar brick and is heated. With this heating, impregnating alloying will take place. However,.in such a case, the expanded air and gas produced within the container will be discharged through the clearance of the seal 6 and therefore there is no danger of the container exploding. Generally, when the container is heated, it will soften and be likely to cause a thermal strain. However, in the present invention, as the container passes through the heating furnace while rotating and, in the case illustrated in FIGURE 3, it is borne by the roll 8 between the furnaces, and any thermal strain will be well balanced and substantially no trace of any strain will be seen. While the container passes through the heating means, the steel plate contained in the container will be treated to the temperature and time required for diffusion coating and therefore an impregnating alloy layer will be uniformly formed on the surface of the steel plate. Then the container enters the cooling means and is water-cooled from the outside surface by the shower 12. In chromizing, this quenching is especially important and serves to increase the ductility of the diffusion layer.

The results of tests of the product produced in the above were as follows:

Thickness of the chromium impregnated Secondly, in the case of colorizing, 1 is a tubular container having an outside diameter of 12 inches, a length of 7 meters and a thickness of 9 mm. (This apparatus is adapated specifically to a large outside diameter). As was the case in chromizing, the container is charged with articles to be colorized, for example, oxygen sucking pipes together with an impregnating agent. An FeAl powder and ammonium chloride NH Cl are used for the impregnating agent so as to be uniformly in contact with the entire surfaces of the articels to be processed.

The container 1 while rotating is conveyed from the position A to the position C.

13 and 14 are barrel type heating furnaces. The furnace 13 which is passed through first is a preheating furnace in which the temperature is kept at 1,000 C. The furnace 14 which is thereafter passed through is a heating furnace in which the temperature is kept at 1,100" C. In such case, the bodies of the furnaces 13 and 14 are kept at the respective required temperatures since before the entry of the tubular container, the containers pass successively through the furnaces While rotating.

The rotating and advancing velocities of the tubular container are as follows:

Rotating velocity r.p.m. 1 Advancing velocity m./hr. 1.5

Such rotary rolls as are represented by numeral 15 in FIGURES 4, 5 and 6 are used as devices for rotating the tubular containers and at the same time conveying them in the direction indicated by the arrow. As evident from FIGURE 5, a slight angle with respect to the tubular container 1 is imparted to the rotary rolls such as, an angle of 1.5 degrees.

As in FIGURE 4, four rolls 15 serving to rotate and convey the containers are fitted in parallel as a set and there are provided four of such sets in position A, four in position C and one between the furnaces 13 and 14. As shown in FIGURES 5 and 6, as each container 1 is supported by two rolls, four rolls constitute a set for two containers. However, it is possible to support two containers with three rolls. Sixten of such rolls in each of the positions A and C and four between the furnaces 13 and 14 are rotated by any mechanism.

In this example, when two tubular containers were set in parallel as in FIGURES 5 and 6, it took 6 hours and 30 minutes to complete the heating operation from position A to position C. This is about half of the operating time taken in a generally used conventional box type furnace. In the present example, air-cooling was used for the cooling device C.

The thickness of the aluminum impregnated alloy layer of the processed article oxygen sucking pipe obtained in this example was 0.3 to 0.27 mm. Such slight thickness error is very hard to obtain in the case of heating and treating a large quantity in the box type furnace. That is to say, as the tubular container is always rotating, the heating temperature will be uniformly conducted. Further, the container is so uniformly air-cooled in the cooling device C that no strain will be seen to be produced in the container. 16 is a heating device for the furnace and 18 a base stand.

The experimental results of the actual use in a steel manufacturing factory of the oxygen sucking pipe made in in the present example are follows:

This example Comparison Thickness of fused layer, mm 0. 06 0. l2 Thickness of impregnated layer, mm 0.3 0. 78 Total thickness of the layers, mm 0. 36 0. 90 Experimenting time, minutes 42 33 Total length of consumption, mm 3. 020 3. 490 Length of c0nsu1nption/min., mm 71. 9 105. 8

case, preheating means are'provided between the conveying means and the heating means.

Heavy oil, town gas, propane gas, butane gas and electric heat can be used for the heating source.

Either water cooling or air-cooling can be adopted for the cooling means whereby a coolant is jetted on to the entire outer periphery of the container 1 by using a hose having jetting orifices in place of the illustrated means. Also, a chain conveyor or a carriage can be used in place of the illustrated roll-conveyer.

In a case where the use of a cylindrical container is undesirable due to the shape of the article to be processed, a square sectioned tubular container can be used.

One or more barrel-shaped heating furnaces can be used and a plurality of containers can be simultaneously inserted.

The container can be of a double-walled structure so that the article to be processed and the impregnating agent may be inserted between the inner tube and the outer tube.

The following facts can be enumerated as features of the diffusion-coating process using the present apparatus.

(1) The temperature distribution for the cotnainer is so uniform that the impregnated layer will be produced uniformly.

(2) As quick heating and continuous operation are possible, the required time will be reduced and fuel saved.

(3) Any thermal strain of the container can be balanced and the container repeatedly used. 1

(4) As the required temperature is always maintained without the repetition of cooling and heating, damage to the heating furnace body will be reduced.

(5) In chromizing, the ductility of the diffusion layer will increase due to quenching.

(6) In colorizing, the antioxidizability of the diffusion layer will be increased.

(7) The aging of the impregnating metal will be reduced by the reduction of the operating time.

\Vhat I claim is:

1. A heat treatment apparatus for the diflusion coating of the surface of metal articles, comprising a tubular metal container having a closed end and an open end, said container being adapated to be charged with the article to be coated and an impregnating agent through the open end, a mortar brick sealing the open end of the container and serving as an exhaust port for gases developed within the container, a conveyor for said containers including a plurality of rolls arranged obliquely to the direction of travel of the container for moving the container axially while imparting rotation thereto around the containers axis as a center, heating means located in the path of movement of the container along the conveyor in which the container is heated while rotating and moving axially therethrough thereby coating the surface of the article with the gases developed being discharged through the exhaust port, and a cooling means located in the path of movement of the container along the conveyor following said heating means for cooling the heated container.

2. The heat treatment apparatus as claimed in claim 1 including a second heating means located in the path of movement of the container intermediate the first named heating means and the cooling means with the first named heating means being a preheating furnace and the second a heating furnace.

References Cited by the Examiner UNITED STATES PATENTS 3,108,022 10/1963 Church 118-69 X FOREIGN PATENTS 1,237,713 6/1960 France.

778,745 7/1957 Great Britain.

CHARLES A. WILLMUTH, Primary Examiner. J. P. MoINTOSH, Assistant Examiner. 

1. A HEAT TREATMENT APPARATUS FOR THE DIFFUSION COATING OF THE SURFACE OF METAL ARTICLES, COMPRISING A TUBULAR METAL CONTAINER HAVING A CLOSED END AND AN OPEN END, SAID CONTAINER BEING ADAPTED TO BE CHARGED WITH THE ARTICLE TO BE COATED AND AN IMPREGNATING AGENT THROUGH THE OPEN END, A MORTAR BRICK SEALING THE OPEN END OF THE CONTAINER AND SERVING AS AN EXHAUST PORT FOR GASES DEVELOPED WITHIN THE CONTAINER, A CONVEYOR FOR SAID CONTAINERS INCLUDING A PLURALITY OF ROLLS ARRANGED OBLIQUELY TO THE DIRECTION OF TRAVEL OF THE CONTAINER FOR MOVING THE CONTAINER AXIALLY WHILE IMPARTING ROTATION THERETO AROUND THE CONTAINER''S AXIS AS A CENTER, HEATING MEANS LOCATED IN THE PATH OF MOVEMENT OF THE CONTAINER ALONG THE CONVEYOR IN WHICH THE CONTAINER IS HEATED WHILE ROTATING AND MOVING AXIALLY THERETHROUGH THEREBY COATING THE SURFACE OF THE ARTICLE WITH THE GASES DEVELOPED BEING DISCHARGED THROUGH THE EXHAUST PORT, AND A COOLING MEANS LOCATED IN THE PATH OF MOVEMENT OF THE CONTAINER ALONG THE CONVEYOR FOLLOWING SAID HEATING MEANS FOR COOLING THE HEATED CONTAINER. 